Nowadays, in the field of a member such as a cutting tool, an abrasion resistant member and a slide member of which abrasion resistance, slide performance and fracture resistance are required, there is a method for improving abrasion resistance, slide performance and fracture resistance by forming a coating layer on the surface of a substrate which is made of a sintered alloy such as cemented carbide and cermet, a high hardness sintered body such as diamond and cBN (cubic boron nitride) or ceramics such as alumina or silicon nitride.
In addition, investigations are being actively conducted on a method for forming a nitride layer which mainly consists of Ti or Al as a coating layer described above, by using a physical vapor deposition method such as arc ion plating and sputtering, and on improvements for prolonging a tool life. There have been various kinds of improvements in addition to the chemical elements for the coating layer of the tools the surfaces of which are coated in order to cope with changes in the environment of cutting operation including an increase in cutting speed and with the diversification of materials to be cut.
For example, Japanese Patent Application Publication No. 2008-264975 discloses a tool consisting of a substrate the surface of which is coated with a film of such as TiAlN, a Ti content being larger on the flank face of the tool than on the rake face.
In addition, Japanese Patent Application Publication No. 2002-346812 discloses a TiAlN base hard film having a thickness of 1 μm or more and 5 μm or less with which the surface of a substitute is coated, the fraction of coarse particles having a diameter of the film thickness or more existing in the hard film being 5 area % or less, and the roughness Ra of the surface of the film being 0.1 μm or less or the roughness Rz of the surface of the film being 1 μm or less.
Moreover, Japanese Patent Application Publication No. 11-302831 discloses a hard film of (TiNbAl)N and so forth with which the surface of a substrate is coated, and Japanese Patent Application Publication No. 2005-199420 discloses a hard film, the film containing (TiAlNbSi)N and so forth and consisting of a multilayer consisting of layers having different contents of Si and Nb due to different methods for forming films.
The following is a list of the aforementioned background art:    PTL 1: Japanese Unexamined Patent Application Publication No. 2008-264975    PTL 2: Japanese Unexamined Patent Application Publication No. 2002-346812    PTL 3: Japanese Unexamined Patent Application Publication No. 11-302831    PTL 4: Japanese Unexamined Patent Application Publication No. 2005-199420
However, even with the contexture according to Japanese Patent Application Publication No. 2008-264975 in which a Ti content is larger on the flank face than on the rake face, the heat resistance and the oxidation resistance of a coating layer are insufficient on the rake face and fracture resistance is insufficient on the flank face.
In addition, in the case of the contexture according to Japanese Patent Application Publication No. 2002-346812 in which the fraction of coarse particles is decreased as much as possible, there is an increase in the temperature of the hard film due to entire abutting of chips to the hard film caused by the small roughness of the surface, which results in progression of crater wear and in there being a problem of a decrease in abrasion resistance.
Moreover, even with a composition containing Nb as the third metal in addition to TiAlN according to Patent Literatures 3 and 4, although abrasion resistance is increased, more increase is needed, and, in particular, there are cases where abrasion rapidly progresses due to chipping, fracture or an increase in temperature caused by welding of a workpiece and so forth. Therefore, further increase in abrasion resistance is desired.
An object of the present invention is to solve the problems described above and to provide a cutting tool composing of a coating layer which can locally show an ideal cutting performance.